Among extrusion presses, a direct-type extrusion press that supplies and extrudes a billet in a state where a container is fixed is configured conventionally as follows. That is, the extrusion press is provided with an extrusion stem that is driven by a main ram and moves back and forth in the axial direction and a cylindrical container comprising an inner orifice into which the extrusion stem is inserted so as to be capable of moving back and forth. On the opposite side of the extrusion stem of the container, a die unit is incorporated in a die cassette and the die unit includes a die and a die backer inserted inside a die ring, and a bolster. Above the contact surface between the container and the die, a discard cutting device having a shear blade that is driven by a drive device and moves back and forth in a direction intersecting the direction of extrusion is provided.
Due to such a configuration, when, for example, a cylindrical billet is supplied into the inner orifice of the container and the extrusion stem is moved forward by the main ram, the billet pressed by the extrusion stem is extruded from the die orifice of the die unit and a product in a predetermined shape is produced. After the extrusion of the product is completed, when the container is moved in the direction in which the container is separated from the die, the discard, which is residue (left over) as a result of the extrusion, projects toward the side of the container from the orifice of the die, and therefore, the shear is lowered to shear the discard by the shear blade, and thereby, the discard is recovered and the product can be taken out in the direction of extrusion.
The die unit including the die and the die backer inserted inside the die ring and the bolster is incorporated in the part of the center axis of the die cassette. Then, a top part space for exchanging a die unit is provided over the die cassette so as to facilitate the exchanging of the die unit when the die cassette slides and moves and a die unit is assembled in the die cassette or taken out therefrom (i.e. exchanging of the die unit) at the outside of the device, and the front surface of the die ring is held by a fixing metal fitting in the shape of a horseshoe attached to the die cassette.
As described above, the die unit is placed in the die cassette, and therefore, when the discard and the product are cut off from each other, the shearing force acts in the downward direction and the rear end part of the die rises and inclines and rotates. Accompanying this, the upper end part of the die cassette also tends to incline and rotate toward the side of the container. Because of this, the contact surface of the die with the shear blade inclines and it is no longer possible to completely cut off and separate the discard from the product and part of the discard remains on the contact surface of the die with the shear blade. If the container is pressed against the die in the state where the discard is left on the end surface of the die, it is more likely that burrs and a blister occur during extrusion in the next cycle.
In order to solve the above-mentioned problems, there is disclosed a die locking device, which prevents the die from inclining and rotating by moving the upper end part and the lower end part of the die cassette, on which the die unit is mounted, in the direction of extrusion using a rod provided so as to penetrate through an end platen and by tightening the die cassette to the end platen when cutting off and separating the discard from the product with the shear blade. According to this device, it is possible to solve the problem of the inclination of the die cassette. However, the die is not fixed, and therefore, the gap between the die, the die backer, and the bolster constituting the die unit or the gap formed between the die unit and the die cassette cannot be eliminated and there is a problem that the die inclines when the discard is cut and the discard remains on the end surface of the die (refer to patent literature 1).
Further, there is disclosed a die locking device that comprises a pressure metal fitting to prevent a die from inclining and rotating in the axial direction of the die by pressing the top surface part of the die unit. With this device, the top surface of the die is formed into a tapered form from the end platen toward the container and the top surface of the die in the tapered form is pressed by a pressure metal fitting, and thereby, a pressing force acts in the direction of extrusion and in the direction intersecting the direction of extrusion to prevent the die from inclining and rotating. With the configuration of this locking device, it is difficult to set the die top surface into a tapered form and an acting force sufficient enough to press the die unit in the direction of extrusion cannot be obtained, and the gap between the die, the die backer, and the bolster constituting the die unit or the gap formed between the die unit and the die cassette cannot be eliminated and there is a problem that the discard remains on the end surface of the die (refer to patent literature 2).
The supply of a billet to the conventional rear loading-type short stroke extrusion press is performed by a billet loader attached to the bottom part of the end surface on the side of the extrusion stem of the container in a space part provided by horizontally moving the extrusion stem, and the billet conveyed to the loading inlet of the container is sent into the container by the forward movement of a billet pusher installed inside the main ram. Next, when the billet pusher moves back and at the same time, the extrusion stem moves horizontally to the center position of the press and the extrusion stem moves forward, the billet is pressed and the product is extruded in this configuration.
When the extrusion of the billet is completed, the cylinder for moving the container is activated and the container is moved in the direction toward the extrusion stem while moving back the extrusion stem by moving back the main ram. Then, while moving back the container, the shear blade of the discard cutting device arranged on the top surface of the die is lowered to cut off and separate the discard (the residue of the billet after the extrusion) and the product from each other. After the cutting of the discard is completed, the shear blade of the discard cutting device is lifted up and the cylinder for moving container is activated and thereby the container is moved in the direction of the die and the container is made to come into contact with the die to extrude a next billet.
In the conventional short stroke extrusion press described above, a space part is provided between the rear end surface of the container and the tip end surface of the extrusion stem and the separation between a virtual extension line in the vertically downward direction of the discard cutting device and the tip end surface of the stem is made greater by providing the space part than the width (distance in a direction of extrusion) between the front and rear surfaces of the container.
For the conventional short stroke extrusion press configured as described above, it is possible to shorten the moving stroke of the extrusion stem and the device length so as to save space. Further, it is possible to simultaneously perform the movement of the stem slide and the cutting operation of the discard by the discard cutting device, and therefore, the idle time can be shortened and the productivity can be improved (refer to patent literature 3).
Then, in the discard cutting device used in the above-mentioned conventional extrusion press, the shear guide is installed securely on the top part on the side of the die of the end platen via the fixed frame and the shear cylinder is arranged on the top part of the shear guide. Further, on the tip end of the piston rod of the shear cylinder, the shear guide and the shear slide capable of stroking in the vertical direction along the shear guide are installed securely, and the shear blade is attached to the side of the die at the lower end part of the shear slide (refer to patent literature 4).
When the discard is cut by the conventional discard cutting device thus configured, the fixed frame, the shear guide, and the shear slide are bent and deformed at the same curvature by the output of the shear cylinder. Because of this, it is required for the discard cutting device to have great rigidity to reduce the amount of deformation so as to be capable of operating even if the shear slide is deformed when cutting the discard, and therefore, it is difficult to reduce the width (dimension in the direction of extrusion) of the discard cutting device so as to make thin the discard cutting device, and it is not possible to set small the dimensions of the space part configured to make greater the separation between the virtual extension line in the vertically downward direction of the discard cutting device and the tip end surface of the extrusion stem than the width between the front and rear surfaces of the container, that is, it is not possible to reduce the device length of the extrusion press by shortening the moving stroke of the container and extrusion stem. Further, there is a limit to the improvement of productivity by shortening the idle time.
Then, in the extrusion press comprising the discard cutting device configured as described above, the cutting blade surface of the shear blade and the die end surface are not coplanar due to the change in temperature of the die and a gap, etc., between the die unit and the die slide, and the position of the die end surface fluctuates in a range of about 0.5 to 1 mm. Then, when the gap between the shear blade and the die end surface increases at the time of cutting a discard, the quality of the cut surface of the discard is deteriorated.
For example, when there is an annular porthole of the billet on the side of the container of the die, the aluminum alloy within the porthole is cut out at the time of the cutting by the shear blade. Then, at the time of the next extrusion, the air in the space from which the alloy has been cut out is confined in the extruded product and bubbles, i.e., blister occurs in the extruded product. Further, because the cut surface produced by cutting is not uniform and has bumps and dips the alloy has been cut out.
In order to solve the above-mentioned problems, there is disclosed a technique to solve the above-mentioned conventional problems by installing the shear cylinder for cutting a discard, which is attached facing downward to the frame provided on the side of the container of the end platen that holds a die, in the direction of extrusion and in the opposite direction of extrusion so as to be capable of rotating and by providing a pressing device having a tilting/rotating cylinder capable of adjusting the gap between the shear blade and the die end surface and a roller device to the frame. As a result, the shear precision can be improved by adjusting the gap between the shear blade and the die end surface to obtain an excellent cut surface (refer to patent literature 5).
In the above-mentioned conventional extrusion press provided with a discard cutting device in which the shear cylinder inclines and rotates, before the cutting of a discard is started, a gap is ensured between the die end surface and the shear blade and when the discard is cut, the whole of the shear cylinder is inclined and rotated by the pressing device so that the shear blade is pressed against the die end surface. With such a configuration, the shear cylinder attached apart from the rotation axis of the shear cylinder oscillates considerably and pressure oil is supplied to the cylinder via a flexible hose having flexibility. The lifetime of the flexible hose is short compared to that of the pipe made of metal and periodic exchange is required.
Further, because in this configuration, the shear cylinder is supported pivotally by the frame provided to the end platen and inclines and rotates, the supporting part receives all of the reaction forces at the time of cutting a discard, and therefore, the device is complicated and has a large steel structure so as to reduce the deformation due to the reaction force at the time of cutting a discard, resulting in the high manufacturing cost.